The goal of this proposal is to understand the mechanisms used to create the circuitry of the mammalian retina. Specifically, experiments are aimed toward understanding the role of the transcription factors Islet-2 (Isl2) and specific AT-rich DNA-binding protein 2 (Satb2) in the specification of distinct types of retinal ganglion cells (RGCs). RGCs are the output neurons of the retina and are affected in several retinal diseases such as glaucoma and optic nerve hypoplasias. There are numerous functional types of RGCs in the mammalian retina, each participating in a retinal circuit that encodes a specific aspect of the visual scene, such as motion, spatial patterns, or color. This functional specificity is derive from distinct RGC morphology and selective synapse formation with other cell types; however, how both are established during development remains unclear. Our experiments use a combination of mouse transgenic technology, in vivo physiological electrical recording and imaging techniques, and anatomical tracing. We focus on Isl2 and Satb2 because their expression is restricted to specific RGC classes, thereby suggesting a specific function. In Aim 1 we will determine which types of RGCs express Isl2 and Satb2 using both morphological and physiological criteria. Our hypothesis is that each TF specifies a common receptive field property of RGC types; for example, that Isl2+ RGCs are On and Off RGCs, while Satb2 RGCs may constitute direction selective cell types. Aim 1a is to determine Isl2 expression in mice expressing GFP in defined RGC subsets. Aims 1b and c together aim to classify all Isl2+ RGCs based on morphological and physiological criteria. In Aim 2 we will determine if Isl2 and Satb2 are necessary and sufficient for the RGCs to differentiate into their normal cell types by specifically removing Isl2 or Satb2 from the retina and by ectopically expressing them in developing RGCs. We will then determine the morphological and physiological properties of the resulting RGCs using a variety of physiological and morphological criteria. Our approach to study RGC differentiation will use our knowledge of the structure and function of different genetically-labeled RGC types to identify transcription factors that lead to their differentiation. This will further our understanding of how different retinal circuits arise during development; thi in turn is likely to have practical benefits in understanding the consequences of diseases that affect RGC function. In addition, successful therapies for treating retinal diseases will depend on the restoration of damaged visual circuits, making knowledge of the development of these circuits essential for designing therapeutic strategies and assessing functional recovery. PUBLIC HEALTH RELEVANCE:! In this grant we propose experiments designed to understand the mechanisms by which a common pool of retinal ganglion cell progenitors gives rise to distinct functional types of mature RGCs, each of which participates in a unique neural circuit that encodes a specific aspect of the visual scene: experiments proposed in this grant use a combination of mouse molecular genetics and state of the art neural recording technology to determine the role of the transcription factors Isl2 and Satb2 in RGC functional specification. Upon completion of the proposed aims, we have will insights into how different retinal circuits arise during development: increased knowledge of the molecular control of RGC development is likely to have practical benefits in understanding the consequences of diseases that affect RGC function. Successful therapies for retinal diseases will depend on the restoration of damaged visual circuits, making knowledge of the development of these circuits essential for designing therapeutic strategies and assessing functional recovery.